The Elder Scrolls V: Skyrim

I have been happily playing skyrim for a while now, but up until a few days ago when i tried to open it up a message popped up saying that there where some data missing or something like that the message displayed a link bringing me to some info on the problem; it told me to exit steam then look through my steam folder, delete the appcache file, restart my computer then reopen skyrim on steam, so i did everything it said up untill the point when i clicked "play" all of a sudden anouther message pops up saying:

"failed to initialize renderer. Your display doesn't support the selected resolution. Please set a different resolution in Skyrim's launcher under 'Display Settings'."

What to do from there? I have no idea how to do any of that.Any help would be great thanks

You should be able to change the settings before you start the game, click play and you'll see the launcher that opens, play, options, data files, tech support, etc. select options and change the screen resolution there.